Reliable high gain amplification is often required for a variety of radar applications, such as missile seeking applications, phased arrays and other high frequency operations. Such systems typically operate at frequencies above Ka-band, which is from about 18-40 GigaHertz (GHz). Frequencies above 40 GHz are referred to as millimeter frequency bands. It would be desirable to operate such systems at high frequencies well above 50 GHz and approaching for example, 100 GHz and above. Lower frequency devices are also desired in the 1-24 GHz range for wideband electronic warfare (EW), jammer and decoy applications. Prior art structures providing amplification at high frequencies have proven unsatisfactory and very few devices can even operate at high power above 50 GHz. Therefore, in order to improve power output and bandwidth, new amplification devices are needed.
Traveling wave devices have been employed in the prior art. Such devices have been designed using Gallium arsenide (GaAs) fabrication techniques. Prior art devices use Gallium arsenide substrates using MESFET or pHEMT device technology. For example, reference is made to U.S. Pat. No. 4,733,195 entitled, “Traveling Wave Microwave Device” issued on Mar. 22, 1988, to Hua Q. Tserng et al and assigned to Texas Instruments, Inc. That patent describes a traveling wave transistor structure with input and output transmission lines terminated with unmatched impedances to improve high frequency response by reflection and phase shift. Embodiments include employing a MESFET structure traveling wave transistor with periodically spaced gate feeding fingers. The Gallium arsenide (GaAs) structures include a plurality of cascaded FET devices to implement a traveling wave amplifier. To achieve higher gain, many FET devices may be cascaded. Based on the traveling wave operation, a large gain can be obtained. However, operation of such GaAs devices is limited in power density and bandwidth. In prior art devices the capacitance between the gate and source electrodes (Cgs) of such FETs is very high and the power is limited by the voltage breakdown of the devices. It is desirable to achieve extended frequency range, improved bandwidth, improved gain and provide a device which is small and operates at higher efficiency. Such attributes would enable one to design devices which have reduced size, weight and power consumption.